Method of making spinnerettes



Jan. 9, 1968 B. E. THOMPSON METHOD OF MAKING SPINNERETT ES Filed April 28, 1966 0 3 v w I,

United States Patent 3,362,265 METI-IGD OF MAKING SPINNERETTES Bobby Eugene Thompson, Draper, N.C., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Apr. 28, 1966, Ser. No. 545,932 3 Claims. (Cl. 76-107) This invention relates generally to the production of filaments from synthetic linear polymers and, more particularly, to the fabrication of spinneret plates through which the filaments are spun.

It has always been a costly and time-consuming operation to make the minute spinning nozzles required to produce fine filaments. Such nozzles usually include entry and transition lengths, as well as -a capillary. The term capillary" is used to define the cylindrical terminal length in which the extrudate is sized and shaped. Better filament quality is achieved when the capillaries are punched rather than drilled. Better filament uniformity is achieved with longer capillaries. Although it is becoming increasingly important to improve filament uniformity via this route, high tool breakage has made it economically unfeasible to punch capillaries with lengthto-diameter ratios above -221.

The general objective of this invention is to obtain more uniform filaments. Specifically, the objective is to provide an improved method for making long, straightsided capillaries in spinning nozzles. It is a corollary object of the present invention to reduce tool breakage to a minimum.

The noted objectives have been achieved in the fabrication of a spinneret plate having at least one nozzle beginning in an entrance hole and terminating in a capillary. The capillary is prepared by stamping the plate thickness remaining after fabrication of the entrance hole with at least two punches, successive punches having lesser cross sectional dimensions and increased effective lengths. The first punch is sized for substantial corresponding with and has an effective length less than that of the eventual capillary. The last punch has an effective length greater than that of the capillary.

Other objectives and advantages will be apparent from the following specification wherein reference is made to the accompanying drawing in which FIGURE 1 is a fragmentary sectional view through a spinneret plate and FIGS. 2-7 are enlarged fragmentray views of the capillary area during various stages of its preparation.

A typical spinneret plate has a plurality of nozzles, one of which has been shown in FIG. 1 to extend through plate 10 from its back side 12 to the face 14. As illustrated, nozzle 16 has an entrance hole which includes both an entry length 18 and a transition length 20 and which terminates in a capillary 22 presenting an orifice 2-4 in face 14.

Entry and transition lengths 18, 20 are usually fabricated in one or more drilling steps and finished with a counter-sink punch. Plate 10 is then placed on an anvil plate 26 which has a clearance hole 28 directly beneath the apex of transition length 20. A first punch having a diameter approximately the same as the final orifice size and an effective working length which is considerably less than the final capillary length is used to pre-punch or start capillary 20, i.e., to stamp the thickness of plate 10 remaining after fabrication of transition length 20 and to thereby form the first capillary portion 30 shown in FIG. 3. Except for its relative short effective length, this punch is typical of those used in single-step punching techniques of the type disclosed by Thomann in U.S.P. 2,709,492.

As shown in FIG. 4, a second punch 32 having a diam- 3,362,255 Patented Jan. 9, 1968 eter very slightly less than the diameter of the first punch is inserted into capillary portion 30 which provides support to the punch so that its unsupported length is relatively short. After completion of the second stamping step, the partially formed capillary is as shown in FIG. 5. Below the first capillary portion 30, there is a second capillary portion 34 and a slight protuberance 36. After removing this protuberance from face 14 by rubbing on an abrasive paper supported on a flat plate, the spinneret plate 10 is placed on a thin backup sheet 38, typically made from aluminum. Both are placed on plate 26. A third punch, whose size is slightly smaller but whose length is considerably longer than the second punch, is now used. Capillary portions 30, 34 support and prevent buckling of this long punch. After the third stamping step, capillary 22 is as shown in FIG. 6. It is, of course, recognized that these enlargements are considerably out of scale to show clearly the variations in sizes which actually are quite minute, on the order of 0.0001" in diameter. The size variation should be as small as possible to provide adequate support but large enough to enable a punching lubricant to escape as the punch moves into plate 10. Note that the third capillary section 40 extends into a second protuberance 42. A second finishing step is used to remove protuberance 42 and presents the orifice 24. In this embodiment, three punches are used and the capillary has three portions 30, 34, 40. A first broach 44 has a ball tip 46 which is approximately the same size as the second capillary portion 34. Broach 44 is forced through the second capillary portion 34 and the third capillary portion 40, providing a sizing and finishing operation. A second broach is used which is sized slightly larger and is approximately the same diameter as the first capillary portion 30. Upon completion of this second broaching step, a final capillary Z2 is made which has a long length, good size control and good finish. If necessary, face 14 is given a final touch-up finishing to insure the proper surface finish and to insure a sharp edge at the intersection between capillary 22 and face 14.

The method disclosed herein provides a longer, straightsided capillary which gives better filaments with reduced tool breakage and fewer rejected plates. Typically, the capillaries have length-to-diameter ratios in the order of 4:1. In addition to the improved quality and uniformity of a given filament, the long capillaries also lead to improved uniformity between all the filaments spun from a spinneret or group of spinnerets. Tool breakage is reduced even though the capillaries are relatively long, i.e., under circumstances which make a single-step punching technique impractical.

Longer capillaries can be produced with additional punching steps or shorter capillaries with fewer punching steps. The number of punching steps is not critical. The essential thing is to provide support to the longer punches to prevent column buckling and thus tool breakage and rejection of costly spinneret plates. Although round punches and a round capillary have been illustrated, the present method can be followed to equally good advantage in the production of capillaries with odd shapes, e.g., trilobal and cross. Other variations and modifications of a similar nature will occur to those skilled in the art without departing from the spirit of our invention, which accordingly is intended to be limited only by the scope of the appended claims.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. In the fabrication of a spinneret plate having at least one nozzle beginning in an entrance hole and terminating in a capillary,

preparation of said capillary by stamping the thickpared by stamping said thickness with at least three of 10 said punches.

3. The method of claim 2 further comprising a finishing step of breaching the capillary with two difierent breaches, the second broach having substantially the same cross-sectional dimensions as the eventual capillary.

References Cited UNITED STATES PATENTS 3,017,789 1/1962 Cobb 76107 3,041,894 7/1962 Cupler 76107 3,227,009 1/1966 Manning et al. 76107 GRANVILLE Y. CUSTER, 111., Primary Examiner. 

1. IN THE FABRICATION OF A SPINNERET PLATE HAVING AT LEAST ONE NOZZLE BEGINNING IN AN ENTRANCE HOLE AND TERMINATING IN A CAPILLARY, PREPARATION OF SAID CAPILLARY BY STAMPING THE THICKNESS OF SAID PLATE REMAINING AFTER FABRICATION OF THE ENTRANCE HOLE WITH AT LEAST TWO DIFERENT PUNCHES, SUCCESSIVE PUNCHES HAVING LESSER CROSS-SECTIONAL DIMENSIONS AND INCREASED EFFECTIVE LENGTHS, THE FIRST PUNCH BEING SIZED FOR SUBSTANTIAL CORRESPONDENCE WITH AND HAVING AN EFFECTIVE LENGTH LESS THAN THAT OF THE EVENTUAL CAPILLARY, THE LEAST PUNCH HAVING AN EFFECTIVE LENGTH GREATER THAN THAT OF THE CAPILLARY. 